[5.4] Doubled slashes in feed link rel="self" href

[muhme]

Steps to reproduce the issue

• Install Blog Sample Data
• Check ?format=feed&type=rss
• Check ?format=feed&type=atom

Expected result

No double slash inside feed link rel="self" href URL, e.g.

<link rel="self" type="application/atom+xml" href="http://localhost:7054/index.php?format=feed&amp;type=atom"/>

Actual result

In both feeds there is still a doubled slash existing, e.g.:

<link rel="self" type="application/atom+xml" href="http://localhost:7054//index.php?format=feed&amp;type=atom"/>

System information (as much as possible)

5.4-dev branch

Additional comments

This is a follow-up to #45592